Local genetic adaptation affects community assembly in zooplankton: An experimental test

Background/Question/Methods

Ecologists try to explain community composition in landscapes as a function of environmental heterogeneity and dispersal limitation, but are often faced with limited success. Priority effects may be an important mechanism that can lead to alternative trajectories of community assembly in identical habitats. Moreover, during colonization of novel habitats, ecological release may foster rapid evolutionary adaptation to local conditions of early colonizing species. We used zooplankton communities and the water flea Daphnia magna as a focal species to experimentally test whether genetic adaptation to local environmental conditions influences community assembly. We allowed a genetically diverse D. magnapopulation isolated from a natural pond to adapt to four contrasting ecologies in outdoor mesocosms during two months, and then compared establishment success of zooplankton species (inoculating diverse zooplankton communities in the mesocosms and assessing the composition of the resulting communities) among mesocosms with adapted and non-adapted D. magna populations.   

Results/Conclusions

We observed that adaptation of the D. magna populations to the local conditions (presence and absence of fish and macrophytes) offered in the mesocosms influenced community assembly in the experiment. We observed significantly higher relative abundances of the focal species in the mesocosms inoculated with Daphnia populations that were allowed to genetically adapt to local conditions during two months than in mesocosms inoculated with non-adapted Daphnia populations. This was observed in all four ecologies offered. Variation among replicates in the actual community composition was large, and the focal species got extinct in a number of experimental units. Overall, the influence of adaptation in the focal species was highest on the abundances of species that are expected to compete with the focal species, such as other Daphnia species and large-bodied zooplankton such as Simocephalus. Our results show that micro-evolutionary adaptation to local environmental conditions may impact community assembly and strengthen priority effects. Even though we only allowed two months of genotype sorting in our experiment, the adapted populations of the focal species performed significantly better in the face of immigrants. We argue that evolution-mediated community assembly is likely to be common in natural metacommunity settings.